I just looked in google for a random mp3 bit rate blind test, took it and came here to look for a post just like this!
I took the mp3ornot 128 vs 320 kbps test. I used just my laptop's soundcard and sennheiser HD 598. It was really easy to tell both apart and got a consistent correct score. I had a little handicap; my left ear can register up to 22 Khz (according to the horrible, excruciating, and painfully boring 40-min sound test with the audiologist my workplace forces us to take) so in two of those songs there was a certain pitch at the end of high notes that wasn't present in the more compressed file. Bass impact and general "noise" shows off which one is the lower quality too. There are some clear artifacts at the end of some notes that give away the lower quality compression, too.
But the most interesting thing I found about this sound test is the fact that it was far easier to determine which was the lower quality file not by asking myself which sounds better, but which sounds worse, which isn't the point of having the pleasure of listening to music, is it? AAC and Vorbis at 128 kbps sound pretty good with far less artifacts and should do a good job of reducing the size of not so musically demanding (to call it something) files.
Edited by Arkyle - 9/30/12 at 4:34pm